We all know where the north pole is, right?

It’s there. Easy.

Well, what if I gave you a traveling stipend and asked you to find your way there? You might have more trouble than you think. And not because of the weather, or hungry polar bears.

But because the true, geographic north pole is actually pretty hard to find. Or at least it is to humans, who have spent millennia working out a bunch of techniques to determine roughly where “north” is. But several other animals are experts at finding true north, and it’s thanks to an invisible pattern in the sky. [♪ INTRO] North is so important to the history of navigation, it’s sometimes the only direction you find labeled on a map.

But actually finding true north has never been straightforward. Take navigating by the stars, for example. It’s a classic technique used by cultures around the world for millennia.

And for the past few hundred years, if you wanted to find true north, you could get most of the way by pinpointing the star Polaris and following it until it’s directly over your head. But not only would you not find yourself exactly at the North Pole, such a technique only works when the sky is dark, and sufficiently cloud-free. Meanwhile, a compass can’t tell you where a geographic pole is.

It tells you where a magnetic pole is. And not only is Earth’s northern magnetic pole about 450 kilometers from true north right now, its position is constantly changing. Now, we can and do correct for this offset, but there’s another hitch.

Since compasses are affected by magnetism, they can be led astray by nearby magnets, or even iron-bearing rocks. Meanwhile, for those of us who prefer to navigate using GPS, I’m sorry to inform you that satellites aren’t 100% perfect either. Since they’re in orbit high above the Earth, their readings can get thrown off by changing solar activity, and for lack of a better term…space weather.

So even with all our technological advances, humans still struggle with finding true north. But for many other animals, it’s a piece of cake. For example, back in the early 1900s, scientists hypothesized that certain ant species used the Sun’s position in the sky in order to navigate.

Basically, by using some combination of shades and mirrors to change where the Sun appeared to be, researchers could get their ants to take different paths while trying to get home. But over the years, we came to realize those ants weren’t really paying attention to the Sun’s physical position. Instead, they were looking at something that’s practically invisible to the human eye: how sunlight was polarized.

Now, technically humans can see light that is polarized, in more ways than one. First, the term polarized, or more specifically, linearly polarized, just refers to the fact that all the light waves are vibrating along a single plane, instead of radiating in every direction willy nilly. Plus, if we look really, really, hard, we can also kinda tell when two bunches of light are polarized differently from one another.

But certain ants are way better at that second part. And in one paper published back in 2006, researchers trained a bunch of desert ants on either direct sunlight, polarized skylight, or both, and looked at how this affected their navigation skills. And while it was clear these ants can use both the Sun and polarization data, the latter appears to take precedence.

For example, the ants that were trained using both light sources, and then forced to find their way home using only sunlight, had a bit of a struggle. But it’s not just ants that can tell how light is polarized. Some migratory songbirds can, as well.

And to travel those great distances without winding up in completely the wrong place, they can continually update their knowledge of where north is based on patterns of polarized light that stretch across the sky. This is skylight polarization, and it’s created by the same process that makes the sky blue. Before sunlight can hit stuff on Earth’s surface, like your face, it has to get through the atmosphere.

And on its way through the atmosphere, most of that light is going to bounce off a particle or twelve. So the light waves wind up getting scattered in a bunch of different directions. And the shorter the wavelength of light, the more it gets scattered.

But in getting scattered, light picks up a particular polarization, and the pattern in the sky is global… Or whatever fraction of the globe is being illuminated by sunlight, including all the stuff bouncing off the Moon. And that means that depending on exactly where you’re standing, the pattern you look up at will be a little different. Now again, as a human you can’t actually see that pattern.

But animals like ants and birds can. And they’ve managed to turn it into their own kind of sky map. The question is, can we follow in their footsteps?

And the answer is, yes. Asterisk. Scientists do have ways of detecting skylight polarization.

And they know what it looks like as someone approaches true north. See, for everywhere except the north and south geographic poles, the sun’s distance from the horizon changes over the course of a single day. The biggest change happens at the equator, and the amount it changes will decrease as you move toward either pole.

But no matter how much that position changes, the fact that it does at all affects how much of the light near the horizon is either vertically or horizontally polarized. At sunrise, most of the light at the horizon will have a vertical polarization. But as the Sun keeps rising and time ticks towards noon, that mostly vertical polarization at the horizon has swapped itself out for being a mostly horizontal polarization.

And The same thing happens as we approach sunset, but in reverse. And then rinse and repeat the day after that. And the day after that.

But if you plop yourself down at either geographic pole, this daily rising and setting doesn’t happen. So the polarization pattern around you never really changes. Instead, it just rotates around this invisible point way above your head.

So for every latitude on Earth, with the right equipment you can basically take a few snapshots of polarized skylight at different points in time and work out your position relative to the nearest pole. One team tested this out and published their results back in 2023. They used a special camera and an algorithm dubbed SkyPole, and could figure out where true north was within a few degrees.

Now that might not sound very impressive when you hear other techniques can tell you true north to within 0.1 degrees. But those use skylight polarization in addition to other datapoints. This SkyPole team is trying to pinpoint north just based on polarization.

It’s a simpler method, and it’s also brand new! So, let’s give ‘em a chance to finesse it. According to one of the researchers, this technique could supplement navigation methods that we already use, in places like the open ocean where you don’t have physical landmarks to help keep track of where you are.

But in the meantime, if you really want to find the North Pole without GPS to guide you as best it can, maybe you should think about channeling your inner fairy tale princess and befriend some ants. Because birds are just a little too cliché. But speaking of the Sun, you may have heard there’s solar eclipse on the temporal horizon.

On April 8th, our Moon is gonna hit that sweet spot in space and block all but the Sun’s atmosphere from view… at least if you’re at the right vantage point on Earth. Which I do not recommend finding by way of skylight polarization. I think GPS is perfectly fine.

A total solar eclipse is truly an awesome sight. But staring at the Sun is a big no-no, so if you want to witness this epic event in its entirety, we’ve got you. Behold, our snazzy eclipse glasses, which meet the right safety standards for you to stare at the Sun during the eclipse without hurting yourself.

But that’s not all! We’ve also got limited edition t-shirts that highlight a bunch of cities in the path of totality. Hopefully all of them will have clear skies on the day!

You can pick one up by heading on over to dftba.com/SciShow. Thanks for watching. [♪ OUTRO]